Active Area Determination of Porous Pt Electrodes Used in Polymer Electrolyte Fuel Cells: Temperature and Humidity Effects

Lindström, Rakel Wreland; Kortsdottir, Katrin; Wesselmark, Maria; Oyarce, Alejandro; Lagergren, Carina; Lindbergh, Göran

doi:10.1149/1.3494220

Cited by 60 publications

(50 citation statements)

References 35 publications

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“…4a and b, respectively. For the Pt sample, the oxidation of CO is similar to what has previously been shown in fuel cell measurements [50], with a distinct stripping peak at 0.64 V. On the PtWO x samples, the oxidation starts at much lower potentials. As seen in Fig.…”

Section: Co Oxidationsupporting

confidence: 83%

Tungsten oxide in polymer electrolyte fuel cell electrodes—A thin-film model electrode study

Wickman¹,

Wesselmark²,

Lagergren³

et al. 2011

Electrochimica Acta

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a b s t r a c tThin films of WO x and Pt on WO x were evaporated onto the microporous layer of a gas diffusion layer (GDL) and served as model electrodes in the polymer electrolyte fuel cell (PEFC) as well as in liquid electrolyte measurements. In order to study the effects of introducing WO x in PEFC electrodes, precise amounts of WO x (films ranging from 0 to 40 nm) with or without a top layer of Pt (3 nm) were prepared. The structure of the thin-film model electrodes was characterized by scanning electron microscopy and Xray photoelectron spectroscopy prior to the electrochemical investigations. The electrodes were analyzed by cyclic voltammetry and the electrocatalytic activity for hydrogen oxidation reaction (HOR) and CO oxidation was examined. The impact of Nafion in the electrode structure was examined by comparing samples with and without Nafion solution sprayed onto the electrode. Fuel cell measurements showed an increased amount of hydrogen tungsten bronzes formed for increasing WO x thicknesses and that Pt affected the intercalation/deintercalation process, but not the total amount of bronzes. The oxidation of pre-adsorbed CO was shifted to lower potentials for WO x containing electrodes, suggesting that Pt-WO x is a more CO-tolerant catalyst than Pt. For the HOR, Pt on thicker films of WO x showed an increased limiting current, most likely originating from the increased electrochemically active surface area due to proton conductivity and hydrogen permeability in the WO x film. From measurements in liquid electrolyte it was seen that the system behaved very differently compared to the fuel cell measurements. This exemplifies the large differences between the liquid electrolyte and fuel cell systems. The thin-film model electrodes are shown to be a very useful tool to study the effects of introducing new materials in the PEFC catalysts. The fact that a variety of different measurements can be performed with the same electrode structure is a particular strength.

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Section: Co Oxidationsupporting

confidence: 83%

Tungsten oxide in polymer electrolyte fuel cell electrodes—A thin-film model electrode study

Wickman¹,

Wesselmark²,

Lagergren³

et al. 2011

Electrochimica Acta

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“…In practical cases, highly dispersed Pt catalysts with large surface areas are extremely important to increase the electrocatalytic reactivity [2][3][4]. The information on the electrochemically active surface area (ECA) of such Pt-based electrocatalysts is essential to derive the specific activity for evaluation and comparison of the different catalysts from various sources [4][5][6][7][8][9]. This is one of the prerequisites to understand the relationship between the catalytic activity and their structure/composition, which are the basis for rational design of highly efficient electrocatalysts for PEMFCs and other electrochemical processes.…”

Section: Introductionmentioning

confidence: 99%

“…The charge densities involved in the electro-adsorption (deposition) and electro-desorption (stripping) of probe species such as hydrogen (H) [5,8,10], copper (Cu), silver (Ag) [8,11,12], carbon monoxide (CO) [9], oxygen (O), and hydroxide (OH) [5], are used to estimate the electrochemically active surface areas (ECAs) of various Pt electrocatalysts, including single crystalline and polycrystalline Pt electrodes as well as carbon-supported Pt nanoparticle electrodes [8,9]. This approach is mainly carried out by cyclic voltammetry (CV) based on a number of assumptions: (1) a saturated adlayer of the probe species is formed in a certain potential region; (2) the stoichiometric ratio between adsorbed species and surface Pt atom is a constant (for example, the ratio for Pt and H is normally assumed to be 1:1 while that for Pt and CO is 1:x, where x= 0.65 to 0.8 depending on the research groups) [9,[13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

“…This approach is mainly carried out by cyclic voltammetry (CV) based on a number of assumptions: (1) a saturated adlayer of the probe species is formed in a certain potential region; (2) the stoichiometric ratio between adsorbed species and surface Pt atom is a constant (for example, the ratio for Pt and H is normally assumed to be 1:1 while that for Pt and CO is 1:x, where x= 0.65 to 0.8 depending on the research groups) [9,[13][14][15][16]. Among these processes, the under potential deposition (UPD) processes of H and some metal cations on Pt electrode surfaces are commonly employed.…”

Section: Introductionmentioning

confidence: 99%

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Determining the Active Surface Area for Various Platinum Electrodes

et al. 2011

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Various methods, i.e., the adsorption/stripping of adsorbed probe species, such as hydrogen (H), copper (Cu), and carbon monoxide (CO), oxygen and hydroxide (O/ OH), potentiostatic CO/H displacement as well as double layer capacitance are exploited to evaluate the electrochemically active surface areas (ECAs) of platinum (Pt) foils, chemically deposited Pt thin film, and carbon-supported Pt nanoparticle electrodes. For the relatively smooth Pt electrodes (roughness factor < 3), the measurements from the stripping of H, Cu, and CO adlayers and CO/H displacement at 0.08 V (vs. RHE) give similar ECAs. With the increase of the surface roughness, it was found that the ECAs deduced from the different methods have the order of CO/H displacement less than the stripping of under potential deposition (UPD) Cu monolayer less than the stripping of the UPD-H adlayer. Possible origins for the discrepancies as well as the applicability of all the abovementioned methods for determining ECAs of various Pt electrodes are discussed, and the UPD-Cu method is found to be the most appropriate technique for the determination of ECAs of Pt electrodes with high roughness factors or composed of nanoparticles with high dispersion.

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“…The cathodic hydrogen adsorption peak was integrated between the baseline near 0.4 V and the local maximum near 0.09 V, assuming a charge of 210 μC/cm 2 . 35 The oxide growth parameters were determined from a CV at 80• C and 75% RH, using a sweep from 0.05-1.00 V at 50 mV/s. …”

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confidence: 99%

A Physics-Based Impedance Model of Proton Exchange Membrane Fuel Cells Exhibiting Low-Frequency Inductive Loops

Setzler

Fuller

2015

J. Electrochem. Soc.

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A physics-based impedance model of a proton exchange membrane fuel cell is developed, incorporating a coupled oxide growthoxygen reduction reaction kinetic model. The oxide layer is shown to produce a low frequency inductive loop that agrees quantitatively with the experimental inductive loop at current densities as high as 800 mA/cm 2 , even when kinetic and mass-transfer parameters are fit from polarization curves and cyclic voltammetry instead of electrochemical impedance spectroscopy. The importance of the inductive loop in explaining both AC and DC results is discussed. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0361506jes] All rights reserved.Manuscript submitted October 31, 2014; revised manuscript received February 16, 2015. Published March 3, 2015 Electrochemical impedance spectroscopy (EIS) is a widely used technique in proton exchange membrane fuel cells (PEMFCs) that separates differential contributions to cell overpotential by characteristic time constants. Analysis of EIS is difficult because there may be dozens of processes involved. It is standard to analyze EIS using equivalent electrical circuit models of the PEMFC, in which several key processes are represented by circuit elements such as the resistor, capacitor, Warburg element, and constant phase element. Fitting the experimental EIS data with an equivalent circuit model and obtaining circuit parameters is straightforward. Often, a close fit can be achieved with relatively few components, especially when constant phase elements are used. However, the challenge becomes determining which processes to include and converting the electrical circuit parameters back to meaningful cell parameters.Although the basic building blocks of equivalent circuits, for example the Randles circuit, have an exact physical interpretation, these elements are often applied to more complex processes without accounting for the differences. The circuits may fit the data perfectly, but the parameters have lost their original meaning. Often, some transport processes are faster than double layer charging, and as a result, are inseparable from charge-transfer resistance. Additionally, slow transport processes often contribute impedance that scales with chargetransfer resistance, rather than being independent. Unfortunately, it is common in the literature to see circuit parameters reported as results without a translation to meaningful physical parameters.An alternative approach is to model the physical processes occurring in an electrochemical cell during EIS experiments. This approach was pioneered by De Levie, 1 who calculated an analytical solution for the impedance of a porous electrode with a potential gradient, assuming linear kinetics and no concentration gradient. Keddam et al. 2 cons...

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Active Area Determination of Porous Pt Electrodes Used in Polymer Electrolyte Fuel Cells: Temperature and Humidity Effects

Cited by 60 publications

References 35 publications

Tungsten oxide in polymer electrolyte fuel cell electrodes—A thin-film model electrode study

Tungsten oxide in polymer electrolyte fuel cell electrodes—A thin-film model electrode study

Determining the Active Surface Area for Various Platinum Electrodes

A Physics-Based Impedance Model of Proton Exchange Membrane Fuel Cells Exhibiting Low-Frequency Inductive Loops

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